Method and device for the absorption of heat in a vacuum coating apparatus

ABSTRACT

An apparatus and method for heat absorption in vacuum coating installations includes an absorber having a line system to supply a coolant. The line system is enclosed by a jacket tight relative to the vacuum chamber, flow spaces are arranged between the line system and the jacket, which are connected to a source of heat exchanger medium so that the line system is flowed around by a heat exchanger medium sealed relative to the vacuum chamber.

The invention concerns a device for heat absorption in vacuum coating installations with an absorber, which has a line system to supply a coolant, as well as a method for heat absorption in vacuum coating installations in which a coolant is guided through a line system and takes off absorbed heat.

For the application of layers on the substrates it is known to carry out coating from the vapor phase or via sputtering with or without chemical reaction with a reactive gas.

Especially during coating from the vapor phase the substrate is not rarely exposed to a significant thermal load. The evaporator source is heated to the evaporation temperature of the evaporation material. The evaporator source then represents a significant heat source.

In the production of photovoltaic layers a semiconducting absorber layer is deposited by passing a precoated glass in a transport direction through a metal evaporator source or past it, which is thermally exposed to a temperature of more than 1200° C. It is then the hazard that the substrate will be overheated or will experience unduly high thermal gradients during passage by the evaporator source in the transport direction.

For this reason there is a need for substrate cooling, which can be achieved with radiation cooling, in which heat-absorbing surfaces or elements are arranged in the radiation vicinity of the substrate. It is also important to absorb radiation reflecting from a substrate, which would lead to heating if not absorbed (“destroyed”). Three different cases can be distinguished here:

-   -   1. The substrate has a high absorption capacity, for example,         E=1 on the top (on one side): The entire radiation power coming         from the evaporation source is then absorbed by the substrate         and leads to its heating. Depending on the temperature level,         the substrate has the capability of radiating heat by heat         radiation if surfaces, whose temperature lies below that of the         substrate, are situated in the vicinity of the radiating         substrate and these surfaces have absorption capacity.     -   2. The substrate has a negligibly small absorption capacity: In         this case the substrate absorbs negligibly small amounts of the         radiation emitted from the evaporation source. Almost the entire         radiation impinging on the substrate is reflected. If the         radiation so reflected is not absorbed by the surroundings, the         temperature of the surroundings goes up and ultimately leads to         heating of the substrate, since now the temperature of the         surroundings can be very high and even small absorption capacity         of the substrate can lead to undesired heating of the substrate.     -   3. The substrate has an average absorption capacity: This is         close to the practical case. Both removal of radiation from the         substrate and removal of reflected radiation make absorption         necessary.

In some coating processes the condition must now be maintained in which a minimum temperature must be set on the surfaces in the process space in order to be able to set the vapor pressure of low-melting materials sufficiently high. Condensation of process materials can occur on colder surfaces. This leads to a situation in which evaporated material is withdrawn from the process, which is then no longer available for deposition to form the desired stoichiometry or must be significantly replenished. A significant loss of material occurs here, which should be limited.

On the other hand, condensation leads to undesired contaminants on these condensation surfaces, which is also connected with bursting, which leads to contamination of the layers.

Ordinarily water is used as cooling medium, which is fed in closed line systems. The water-traversed line systems then represent the absorbers within the vacuum chamber. However, the condition of minimum temperature is violated in principle with such a layout of an absorber.

Either such absorbers cannot be used and the risk of substrate overheating must be tolerated or these absorbers are simultaneously condensers for the vapor of the evaporator source.

The task of the invention is therefore to provide a radiation cooling system and method for radiation cooling of vacuum coating processes with which effective cooling is achieved and condensation is avoided.

The task is solved by an apparatus with the features of Claim 1. Claims 2 to 6 represent favorable variants.

The task is also solved by a method with the features of claim 7. Claims 8 to 16 provide a special embodiment of the method according to the invention.

The invention will be further explained below with reference to a practical example. In the accompanying drawings

FIG. 1 shows a schematic cross section through an absorber according to the invention,

FIG. 2 shows a schematic depiction of the use of an absorber according to the invention in a vacuum chamber and

FIG. 3 shows a schematic view of the use of an absorber according to the invention on the evaporator side.

As shown in 16 the absorber 1 according to the invention has an outer tube 2, which is introduced to a vacuum chamber 4 vacuum-tight through a chamber wall 3. The outer tube 2 is sealed relative to the vacuum chamber.

An inner tube (6) is arranged in the internal space 5 of the outer tube 2. The inner tube (6) is opened on one side to the internal space 5. On its other side the inner tube (6) is connected to a coolant source (not further shown), like the pressure side of a pump. The internal space 5 is connected to a coolant sink (also not further shown), for example, the suction side of a pump so that the coolant flow shown with the arrows occurs. Water is used as coolant so that a temperature lying significantly below the minimal temperature which is 300° C. in this example is set on the outside of the outer tube 2.

The outside of the outer tube 2 is provided with a jacket tube 8 by means of a spacer 7. The jacket tube 8 is also closed vacuum-tight relative to the vacuum chamber 4.

A flow space, namely a narrow gap 9 between the outside of outer tube 2 and jacket tube 8 is created by the spacer 7. This gap 9 is connected to a source for a heat exchange medium, in this case helium, and to a sink so that flow of heat exchanger medium occurs in gap 9. Helium can be used because of its very high heat conductivity. Water is also possible as a good heat conductor. In principle, however, other gases can be used, if their heat conduction for the specific task is sufficient with expert knowledge.

The heat transfer resistance and therefore the temperature on the outside of the jacket tube 8 can be adjusted by the pressure and/or flow rate and/or gas composition of the heat exchanger medium so that it does not surpass a minimum temperature.

Since the heat transported away by the absorber also depends on the pressure of the gas in the gap, this effect can also be exploited by setting the gas pressure so that the desired heat increase (while maintaining a temperature of, for example, 300° C.) is taken off as absorber.

16 shows the case in which the heat is taken off via the helium in the gap and only heat conduction or helium plays a role here. The absorber tube 8 can also be cooled by pumping helium or another gas in circulation and passing it either outside of the exchanger or using the inner water-traversed tube as a heat exchanger surface.

As shown in 15 the absorbers 1 are arranged across the transport direction 10 of the substrates 11, in which the substrates 11 are passed by an evaporator source 14. Since the evaporator source 12 has a very high temperature, the substrates 11 would experience a significant thermal load. The absorbers 1 prevent this.

For heat control of the process heaters 13 are also provided. The chamber wall 3 is protected from the hot processes by heat insulation 14.

The outside temperature of the jacket tube can also be measured via a temperature sensor 15 so that it is guaranteed that the minimum temperature is not fallen short of.

To improve the absorption effect the jacket tube 8 is provided with surface-enlarging elements 16.

As shown in FIG. 3 additional absorbers 17 according to the invention are arranged across the transport direction 10 on the side of the substrates 11 on which the evaporator source 14 is situated. These additional absorbers 17 serve to trap the heat radiation that is reflected on the coating side of the substrates 11.

LIST OF REFERENCE NUMBERS

-   1 Absorber -   2 Outer tube -   3 Chamber wall -   4 Vacuum chamber -   5 Internal space -   6 Inner tube -   7 Spacer -   8 Jacket tube -   9 Gap -   10 Transport direction -   11 Substrate -   12 Evaporator source -   13 Heater -   14 Heat insulation -   15 Temperature sensor -   16 Surface-enlarging elements -   17 Additional absorber 

1. Apparatus for heat absorption in vacuum coating installations with an absorber, which has a line system for guiding of a coolant, wherein the line system is enclosed by a jacket, tight relative to a vacuum chamber, and flow spaces are arranged between the line system and the jacket, the spaces being connected to a source of the heat exchanger medium.
 2. Apparatus according to claim 1, wherein the line system comprises a closed outer tube having a coolant line arranged in an internal space of the outer tube, and the outer tube is provided with a jacket tube arranged spaced via a spacer to form a flow space connected to the source of heat exchanger medium.
 3. Apparatus according to claim 2, wherein an inner tube open to the internal space is arranged in the outer tube and the inner tube is connected to a vacuum source or sink and the internal space of the outer tube is connected to a vacuum sink or vacuum source.
 4. Apparatus according to claim 3, wherein the inner tube is arranged concentrically in the outer tube.
 5. Apparatus according to claim 2, wherein the jacket tube is arranged concentric to the outer tube.
 6. Apparatus according to claim 2, wherein an outside of the jacket tube is provided with surface-enlarging elements.
 7. Method for heat absorption in vacuum coating installations comprising flowing a coolant through a line system to take off absorbed heat, and flowing a heat exchanger medium sealed relative to a vacuum chamber around the line system.
 8. Method according to claim 7, wherein the coolant comprises water.
 9. Method according to claim 7, wherein the heat exchanger medium comprises a gas.
 10. Method according to claim 9, wherein the heat exchanger medium contains helium.
 11. Method according to claim 10, wherein the heat exchanger medium consists of helium.
 12. Method according to claim 9, wherein the heat exchanger medium contains hydrogen.
 13. Method according to claim 12, wherein the heat exchanger medium consists of hydrogen.
 14. Method according to claim 9, wherein the heat exchanger medium contains air.
 15. Method according to claim 14, wherein the heat exchanger medium consists of air.
 16. Method according to claim 7, wherein a temperature difference between the coolant and the heat exchanger medium is controlled by pressure, flow rate and/or gas composition. 